This invention relates to the testing of metal bodies for defects in general and more particularly to an improved testing device for detecting defects in a metal body where the body is moved during testing and cannot be reliably maintained in an accurate position with respect to the testing device.
Co-pending Application Ser. No. 480,424 describes apparatus for detecting defects in a metal body by generating a traveling field such as a rotating or a linearly traveling field in the body being tested and by providing means to sense an asymmetry in the resulting magnetic field occurring due to the induced eddy currents thereby permitting determination of the location and nature of the fault from the electrical signals. In the embodiment disclosed therein faults and irregularities in the body such as cracks, indentations and so on are detected through this asymmetry which is preferably indicated in a neutral line existing between the generator and the transducer. In another embodiment a bridge or differential connection is used.
However, the device claimed therein is not usable for all types of testing which must be carried out. It has been found that for certain types test objects, for example, rolled wire other movable test objects, it is very difficult to keep the test object centered with respect to a differential connection or the like as is necessary with the majority of embodiments disclosed and claimed in the aforementioned application. In view of this, the need for an improved device which can make accurate measurements in such test objects becomes evident.